Method of separating acetylene



Patented Dec. 30, 1952 UNITED STATES PATENT OFFICE METHOD OF SEPARATINGACETYLENE Morris Levine, Tulsa, and Robert M. Isham,

Okmulgee, kla., assignors, by mesne assignments, to Southern ProductionCompany, Inc., Shreveport, La., a corporation of Delaware No Drawing.Application October 19, 1945, Serial No. 623,452

2 sirable characteristics. Such solvent shouldhave a high solvent powerfor acetylene and conversely a low or negligible solvent power foraccompanying gases; in other words, the solvent should be 011$ ar ns. bya number f different 5 highly selective to acetylene as well aspossessing i methgds i fih treat a good solvent capacity therefor. Suchselecggg ges b g rgg magd x012; &2: 8 tivity, as is understood in theart, essentially desage of Such hydrocarbons through a electric ter nmesthe number of absorption steps or cycles are and incomplete combustionof such hydro- 10 wmch are necessary to secure an a9etylene fraccarbonsas for example in the manner disclosed non of predet-er-mmedcon-cemmtlon from lean in the copendmg appiication of Otto p gacetylene-containing gas mixtures. A (idSlIitblG Serial No 540 385 filedJune 1944 new Patent; effective solvent should also be characterized byNo.2466 i317 issued April5 194s. a VaPQrPIIBSSMe 3 temperatures In allsuch methods the reaction product is a 15 so as to mmlmlze vaponmtmnlosses of the S01- complex gaseous mixture containing but a rela- VentSolvent hkewlse should not be ,ther' tively Small percentage ofacetylene Depend molabile and should be chemically stable under mg uponthe particular process employed such the temperature and pressureconditions of exgaseous reaction products contain carbon dioxtractlonand solvent rePovery' me, carbon monoxide hydrogen, nitrogen As a resultof extensive experimentation in this converted hydrocarbons, ethyleneand the like. field It has f bflaen dlscovered theft certam The reactionmixture may also contain benzene, oxygenated derlvatlves of h relatlvely10W naphthalene and other aromatic hydrocarbons mic Weight elements of gup V f t periodic as well as some carbon black. table are unexpectedlyand peculiarly efiicacious In order to commercially utilize theacetylene as selective solventsfor acetylene and abundantly or toconvert it into other valuable and useful satisfy the requirementspreviously set forth. pro u s it is desirable to treat such gases toMore particularly it has been ascertained that of of as the esters,amides and mixed ester amides are i fi' fi "ggziig g f i'gz fig; g gffigespecially valuable for this purpose. Similarly, undis sol ved gases andther after segarating the analogous derivatives of oxy'acids of nitrogendissolved gases from the extracting solution by Such as mtrosyl ammesfunptlon excellelllfly heating and/or reducing the pressure of the solu-The efficacy of the descrlbed roup of comtion. For such acetyleneconcentration or sepapounds for the p'urposes of the Y P can ration,various solvents have been proposed in the readily appreclated fromcons'ldefatlon of past, such as: esters of polyhydric alcohols, estersdata m Table I which Shows t hlgh of polybasic organic acids,polyketones, aliphati bility of acetylene, at the statedtemperature, inm t a d th like, a number of compounds of the group described.

Table I Volumes acetylene Solvent Formula gf" 1 5 33? 701111316 solvent$i tt ii %t%iZY?;-::::::: 8:583? 32 $311? D0 O =PEOC2H99, 35 18. 22'lrl-n-propyl phosphate 0=P 00 111): 26 16.19 'lrl-n-butyl phosphate. 0P (0 04110): 24 13. 16 Tri-oetyl phosphate 0 =P(0C8Hl7)8 28 6. 29tilttiifitlitsasaamr it 3 231?? ethhyllaugdelgt. .H 2Hi)2[ 2Hs)2] islttyl an l eii f OP(OC:H5)2[N(CH3)2] 35 24.93 23332221?f: -??ifiO=P[N(OHzlz]a so 4s. 89 Nitrosyl dimethylam'me 0 =N-N (CH3) 2 30 14. 59

As will be appreciated, a solvent to be satisfactory for the describedconcentration and/or separation of acetylene from such heterogeneousgaseous mixtmgs shouid possess a number of de- As noted previously, adisideratum for this class of solvents is a low solubility for thecoinpohents of the gaseous mixture other than. acetylene. The compoundsn; the type described pre- 3 sent just such "desirable-low solubility asis shown in Table II in which typical derivatives of oxyacids ofphosphorus, namely, tri-n-propyl phosphate andphosphoryl-tri-dimethylamide are theillustrative examples.

Table I1 Volumes 5353 3 3 dissolved e by 1 vol. Gas by 1 phosphoryl.m'n'pwpyl tridimethyl phosphate amide at at 26 C.

Ethylene; 1. 93 2. 16 Carbon Diox1de 2. 79 3. 80 Methane.- i- 0.46 0. 30Carbon Mono 0. 09 O. 14 Hydrogen 0.13 0. Nitrogen. 0.12 1 0. 04

It" wililbe observed from the results depicted in the tables-thatsolvents of theclass described are especially effective for theconcentration of acetylene They present verylow or negligible solventpower for hydrogemcarbon monoxide and nitrogen. This is .aiparticularlydesirable feature because,; as will be seen' subsequently in'Table III;these three gases :areusually the preponderant constituents? of;theeaseous mixture. These solvents? also,ha;ve' but low solventpower formethane ,and eth'ylene. As is apparent from Table I this groupof;solventspossesses high solvent power for acetylene and this coupledwith their marked selectivity establishes them as excellent solvents forthe described" purposes.

The-utilitylaridflefiicacy or these materials as selective, ,Iventsrcra'cetylene'will be more readily appre'ciatd from a consideration oftypical examres t their use. A gas mixture was produced by partial,combust'ion of methane (natural as) The gaseous products werecompressed to 250 p. s; i; an weresubjec'ted to a' countercurrentscrubbing ina bubble tower with-a stream of tri-n-propyl phosphate" atatmospheric temperature: The undissolved gases were discharged from thetop of. the tower andthe solvent; saturated with;gaseouseonstituents,was withdrawn from zb tt mi. Ihes QWenh stripped of the dissolvedgasesby reducing the pressure and neating t esolvent and the evolved gasesanalyzed. The r'esult'sof 'such, treatment, illustratingthestrikingenrichmentlofl the gas in acety- I ene, aresiiown in Tame Inin which the composition of the original gas andthe gas mixture evolvedfrom the solvent are directly compared.

In a second typical example, the same entering gasmixture, as describedabove, was employed. Conditions-of operationwere substantiallyidentibfallwith those described above except that the solvent employedwas phosphoryl-tri-dimethyl amide. The composition. of. the enriched gasevolved from this solvent is shown in Table III. Table HI EnrichedEnriched 7 Original gas gas from i -gg Constituent mixture, Tri-n-propyltridimethfl percent phosphate, amid percent percnt Acct lone." 3.:'073.44 9200 Ethy lene. 0 42 l. 04 0. 51 Carbon dioxide. 2. l2 7. 64 4. 42Methane; 7. 66 4. 54 1.19 C8lb0l1 m0Il0X1d8 10. l. 21 0. 82 Hydrogenuull28.50 4. 77 Nitrogen. 47. 30 V 7. 31 1. 06

Theconcentrations of acetylene canbe fur ther increased by treatment ofthe preliminarily concentrated gas mixtures tabulated in Table III withselective solvents for carbon dioxide. For example, the gas mixtureproduced by treatment with phosphoric-tri-dimethyl amide wasscrubbedthroughmonoethanol amine for selective'extra'ction'ofthe carbondioxide and yielded a product containing 96% acetylene. As will beappreciated, this is sufficiently pure for most commercial purposes.

To determine still further the utility of the improved'class ofsolventsfor producing high concentration of acetylene the enriched gasmixture obtained in Example lil" by-extraction'withphosphoryl-tri-dimethyl amidewas retreated by counterourrent extraction withthis solvent. It wasdetermined that with such a retreatment a gasmixturewas"produced'which contained 97.7% of acetylene and 1.75% of carbondioxide. As will be appreciated, such as gas mixture may be furthertreated in any desired manner to remove the; carbon dioxide: Forexample, the retreated gas mixture mentioned above, and containing97.7%; acetylene was scrubbed with nion'o-eth anol amine for removal@oil-carbon; dioxide as a result of which a purified-' gas containingover 99% acetylene wa-sobtainedv Itis particularly to be noted that thesolvents of the'novel group described-herein are all characterized by arelativelylcw vapor pressure, at ordinary temperatures; fer example,triethyl phosphate boils at 211 Ct at'atmo spheric pressure while thevapor pressure oi phosphoryl tridimethyil amide is but 2mm. at The-greatnumber of compounds of the group describeddistill at temperatures above200 C; at atmospheric pressure without decomposition thus possess thedesired chemical; stabilityfor the described use.

It will be observed that of the phosphorus-containing solvents listed inTable I all but one are compounds containing a phosphoryl group. Byreference to this tableit is apparent that compounds containingthephospho'ryl group arebetter solvents than compounds of approximatelythe samemoiecuiar weight which donot contain such group thiisindioatirig distinct functional specificity of this grou However; evenwithout the presence era phosphoryl rou substances of this generalclass. are'valuable selectivesolvents for acetylene.

Furthermore, just as compounds containing the phosphoryl group have beenshown to have great selectivity for acetylene, analogous compoundscontaining the nitrosyl display similar properties. It is to be notedthat these compounds are derivatives of elements of group V of theperiodic table, with atomic weights of less than 35.

It will be observed that the utility of the inventions is not restrictedto the employment of the improved solvents for separating acetylene fromgaseous mixtures thereof. The invention is available for any purpose inwhich it is desired to employ a solvent having either a high solventpower for acetylene or which is highly selective for acetylene. Forexample, solvents of the present invention may be used in lieu ofacetone or similar solvent to obtain a high concentration of acetylenein acetylene cylinders.

In commercial operations in which acetylenecontaining gases ar'e' to betreated to achieve an enrichment of acetylene the described solvent n a.f

extraction with the preferred solvents may be utilized in conjunctionwith other separation methods adapted to concentrate or remove specificcomponents of the gas being treated. For example, the present method ofconcentrating acetylene may be embodied in a continuous process oftreating acetylene-containing gases produced by incomplete combustion ofhydrocarbons such as is described in copending application, Ser. No.540,385, now Patent No. 2,466,617, heretofore referred to. V

The reaction gas produced in such process comprises a mixture of carbonmonoxide, carbon dioxide, hydrogen, methane, ethylene, acetylene, carbonblack, aromatics such as benzene and naphthalene. This gaseous mixturemay be treated to remove the carbon black as for example, by passagethrough a filter or Cotrell precipitator.

The gas freed from entrained solids may then be passed to a scrubber andscrubbed therein under superatmospheric pressure with a selectivesolvent for the aromatics, as for example with a mixture of petroleum orcoal tar hydrocarbons. This solvent effectively extracts benzene andnaphthalene from the gas stream. This solvent may then be stripped ofthe aromatics and the denuded solvent recycled.

The gas, freed of aromatics, is then preferably compressed to the degreesuitable for the particular solvent employed and the compressed gas isthen contacted in a suitable tower or towers with one of the describedsolvents or suitable mixtures of such solvents. While compression of thegas prior to contact with the novel solvents is desirable it is notessential. The extraction with the novel solvents is preferably carriedout countercurrently and continuously. The solvent with itspreferentially or selectively dissolved acetylene accumulates in thebase of the extraction column and may be passed continuously orintermittently to a stripping unit which is operated under thosepressure and temperature conditions which conduce to separate thesolvent from the dissolved acetylene and other gases. The strippedsolvent may be recycled to the extraction column to contact additionalquantities of gas. The components of the gaseous mixture which are notextracted by the solvent in the extraction column may be withdrawntherefrom and disposed of or. treated in any desired manner.

The gases evolved from the solvent in the stripper may be againextracted with the same solvent or with another solvent of the novelgroup and such dissolved gases may be evolved from the solvent in themanner described. This enriched gas may be further concentrated byremoving the residual carbon dioxide content as by treatment with aselective solvent for carbon dioxide. Obviously, if desired, the carbondioxide stripping may be applied to the gas which is evolved from thefirst solvent stripping operation.

In some circumstances it may be desirable to remove the liquid solventsaturated with acetylene for direct technical or industrial use as, forexample by charging it into pressure cylinders from which the dissolvedacetylene may subsequently be evolved by releasing the pressure.

It will now be appreciated that the class 'of solvents describedhereinare of peculiar utility in this field. Their high solvent power foracetylene is of special value since the reaction gases which are treatedcontain but a minor percentage of acetylene. Such high solvent powerthus insures high extraction with relatively low ratios of circulatedsolvent. Of equal importance is the strikingly high selectivity of thisclass of solvents. As will be observed, this selectivity is most markedas to those constituents of the gas. such as nitrogen, hydrogen andcarbon dioxide which together constitute about three-quarters of thetotal volume of the lean gas.

While specific examples of the improved highly selective acetylenesolvents have been described it is to be understood that these are givento illustrate the value of the general group having the describeddesirable characteristics. The invention thus comprehends the unexpectedeffectiveness of oxygenated derivatives of the low atomic weightelements, phosphorus and nitrogen and particularly their alkoxy andalkyl amine derivatives for the selective solution of acetylene.

We claim:

1. In the concentration of acetylene from gaseous mixtures thereof, thestep of contacting the mixture with a solvent predominantly comprising atrialkylated amide of phosphoric acid.

2. In the concentration of acetylene from gaseous mixtures thereof, thestep of contacting the mixture with a solvent predominantly comprising amixed lower alkyl ester amide of phosphoric acid, said amide containingno free hydroxy groups.

3. In the concentration of acetylene from. gaseous mixtures thereof theimprovement which comprises contacting such mixture with a compound ofthe type in which X is a phosphoryl group, R is an alkoxy group and R1is analkylated amido group 4. In the concentration of acetylene from.gaseous mixtures thereof the improvement which comprises contacting suchmixture with a compound of the type in which X is a phosphoryl group, Ris an alkoxy group and R1 is an alkylated amido group.

5. In the concentration of acetylene from gaseous mixtures thereof theimprovement which comprises contacting such mixture with a compound ofthe type of X-R3 in which X is a phosphoryl group and R is an alkylatedamido group.

6. In the concentration of acetylene from gaseous mixtures thereof theimprovement which comprises contacting such mixture with phosphoryltri-dialkyl amide.

7. In the concentration of acetylene from gaseous mixtures thereof theimprovement which comprises contacting such mixture with phosphoryltri-dimethyl amide- 8. In the concentration of acetylene from gaseousmixtures thereof the improvement which comprises contacting such mixturewith diethyl phosphate mono diethyl amide.

9. In the concentration of acetylene from gaseous mixtures thereof theimprovement which comprises contacting suchmixture with diethylphosphate mono dimethyl amide.

1333951 7 8 1Q; i ;th om;gantrationzoiacstyl nfi 79, 1 as: NIT D $.TA TE TEN eons; t esl thereof: the improvemfi fii Wh Qh Number. Name Data:comprises Qonbact ngvsnch mixture; with dial-KY 1,799,349. Bannister -vApr t m nomplkyljamida. 2,146,448 Scott? --v-.--. b- 71-1939 5 ,1 0,841Dreyfus JLH Qfi' 1:939 MORBISLEV NE; 2, 60;a42 Dreyfus 1 1. 55 3 ROBERTISHAM=- RBIG ATENT Numbfil- Country Date. E ENQ S GJTED 1o 2624M GreatBritain ep.- 17,4921 The following references are: of recordin .theOTHER REFERENCES."

file: of this patnt: I

Be ilstgin, Handbbok of'Org'ani Chemistry, fined. (1922) ,voliipagesfiifij. V V

2. IN THE CONCENTRATION OF ACETYLENE FROM GASEOUS MIXTURES THEREOF, THESTEP OF CONTACTING THE MIXTURE WITH A SOLVENT PREDOMINANTLY COMPRISING AMIXED LOWER ALKYL ESTER AMIDE OF PHOSPHORIC ACID, SAID AMIDE CONTAININGNO FREE HYDROXY GROUPS.